ae oar ee ee eS Pee 
1912] HOLDEN—SAPIN DALES 51 
in the wood formed immediately after injury. Anatomical evidence 
thus shows that there are present in the leaf, petiole, root, and 
wounded tissue of gymnosperms, structures quite unlike those 
normally occurring in the stem; and paleobotanical evidence shows 
that these are primitive features, retained in certain restricted 
localities long after they have disappeared elsewhere. Instance 
after instance could be cited where these two lines of evidence, 
anatomical and paleobotanical, reinforce each other in the gymno- 
sperms. In the angiosperms, however, no such checking up is 
possible as yet, because of the comparative scantiness of fossil 
material. Here the anatomical principles worked out from a 
study of gymnosperms have to be relied on exclusively in tracing 
their phylogeny. 
Another principle of comparative anatomy is that simple con- 
ditions are not necessarily to be interpreted as primitive. This 
is well recognized by zéologists, who regard tunicates as verte- 
brates which, in losing almost entirely their vertebrate character- 
istics, have reverted to a simpler ancestral organization, and as 
degenerate rather than primitive. Or, on the botanical side, Abies 
has as simple normal wood as any known; there are only two types 
of elements present, tracheids and parenchyma, transverse and 
longitudinal. In the roots of all species, however, there are 
specialized resin canals, surrounded by parenchymatous epithelial 
tissue; these are present also in the reproductive axes of certain 
species. Another complication is present in the wounded root 
of at least one species,* where above and below the parenchymatous 
ray cells there are rows of tracheidal cells, forming ray tracheids 
like those of Pinus. Applying the principles of comparative 
anatomy, it is evident that Abies is descended from forms which 
had both resin canals and ray tracheids, and its simplicity of wood 
structure is not primitive, but a result of degeneracy. 
It is the purpose of this paper to present the conditions found 
in certain of the Sapindales, and then to interpret them in accord- 
ance with these principles. For this purpose, four representative 
genera were chosen; Aesculus, Acer, Sapindus, and Staphylea. 
4THompson, W. P. The origin of ray tracheids in the Coniferae. Bort. Gaz. 
50:101-116, Ig10. 
